Small motorcycles, more precisely scooters, incorporating a continuously variable transmission or CVT are well known in the art.
Often, on such two-wheeled vehicles, the CVT is packaged with the engine. This provides a practical layout where the engine and the CVT are provided as a unitary structure. Most of the time on scooters, the CVT casing acts as a swing arm for the suspension of the rear wheel. The CVT belt is located inside the swing arm, connecting both drive and driven pulleys of the CVT. With such a design, the rotational axis of the driven pulley is co-axially located on the axis of rotation of the rear tire.
One disadvantage with this design is that the packaging, although it is convenient, precludes a compact mechanical engine and CVT layout for the vehicle. This is because the swing arm extends toward the rear of the vehicle while the engine is positioned close to the center of gravity of the vehicle. Accordingly, the CVT is positioned a relatively far distance from the vehicle's center of gravity or CG. Since the CVT itself is a heavy component of the vehicle, this arrangement changes the center of gravity of the vehicle to a location that may not be optimal for performance of the vehicle.
Another disadvantage of incorporating the CVT casing as a part of the rear swing arm is that the unsprung weight of the vehicle is increased. It is well known in the art that the dynamic behavior of a vehicle improves when there is less unsprung weight. As a result, increasing the unsprung weight of the vehicle by incorporating the CVT into the rear swing arm negatively impacts on the operational performance of the vehicle, as would be appreciated by those skilled in the art.
In addition, as also is known to those skilled in the art, a compact arrangement for the engine and its transmission (the CVT) is desirable because the vehicle dynamic behavior is better when the mass of the CVT is centered close to the vehicle's center of gravity. Having the CVT casing at the rear of the vehicle is, therefore, not optimal.
There is, therefore, a need for an improved CVT-engine layout over the prior art.
In particular, there is a need, among others, for a compact vehicle construction with a CVT where the CVT does not contribute significantly to the unsprung weight of the vehicle.